Floating roof for liquid storage tanks



1947' J. H. WIGGINS 2,425,771

FLOATING ROOF FOR LIQUID STORAGE TANKS Filed Aug. 19, 1944 mmvrozz.

JOHN H. IGGIN M ATTORNEY Patented Aug 19, 1947 UNITED STAT ES PAT ENT OFFICE 2,425,771 FLOATING 'RUOF FOR IiIQ'UID STORAGE TANKS John H. Wiggins, Chicago, Ill. Application August 19, 1944, Serial No.550',278 1 Claim. (01. ciao- 2 This invention relates to floating tank roofs of the general type or kind disclosed in my-U. S. Patent No. 2,321,058, dated June 8, 1943, which comprise a center pontoon of stiff construction, an annular pontoon of stiff construction, located at the peripheral edge or the roof, and a flexible deck portion bridging the space between said center pontoon andperipheral pontoon, and constructed or disposed so that rain water which falls onto said deck portion, or which is discharged onto same from the top sides of said center and peripheral pontoons, will drain to one or more water outlets that lead from the top surface of said deck portion.

The main object of my present invention is to provide a floating tank roof of the general type or kind above mentioned, whose deck portion is maintained at a progressively increasing downward, slope, from the peripheral pontoon towards the center of the'roof, whereby rapid and eflicient drainage of the roof is assured.

Another object of my invention is to provide a floating tank roof, of improved construction, in which the entire area of the underside of the deck portion-of the roof is effectively maintained in a wetted condition by the liquidon which the roof floats, thereby eliminating rapid or excessivecorrosion of the deck portion, resulting from the accumulation of air or vapor between the deck portion and the roof supporting liquid When said liquid consists of sour or highly corrosive oil.

And still another object of my invention is to attain the highly desirable results above referred to, without increasing the cost of a roof of the general type previously mentioned.

To this end I have devised a floating roof that comprises or which is composed of a stiff annular pontoon arranged at the peripheral edge of the roof, a stiff center pontoon provided with a peripheral rim, a flexible deck portion attached at its outer edge to the outer pontoon adjacent the surface of the roof-supporting liquid, and attached at its inner edge to the lower edge of the rim of the center pontoon, and means for concentrating a heavy load on the center pontoon, so as to submerge the rim of same in the supporting liquid, to a depth sufficient to cause the deck portion to slope downwardly towards the center of the roof, with a progressively increasing pitch as it approaches the rim of the center pontoon. In the preferred form of my invention herein illustrated the concentrated load On the peripheral rim of the center pontoon is obtained by transferring a portion of the weight of the annular pontoon to the center pontoon by means of a plurality of trusses combined with said -poi1- toons. However, I wishit to be understood that iny b'roadidea contemplates the use of anymea'ns, in a roof of the general type or kind previously mentioned, that will 'cause the inner edge of the deck portionof the roof to be submerged 'acdn- 'siderab-le distance in the supporting liquid, even when the roof is noaun normany, with no exoessi-ve rain or water load, for the rimary purpose of maintaining the deck portion in an 111- clined position, with -a progressively increasing downward slope from the outer pontoon, towards therim of the center pontoon at or adjacent to which is located a primar drainoi-itlet, through which water can escape from the topside ofthe roof.

Figure lot the drawings is a fragmentary vertical transverse sectional'view of a floating tank roof embodying my present invention, showing the roof-floating normally with no excessive load thereon; and

"Figure zis a diagrammatic view, illustrating the principle of operation of my present invention, the vertical scale in Figure 2 being approximately four times the horizontal scale.

In the drawings-"C designates the center pontoon, A designates the annular pontoon at the peripheral edge of the roof B designates the deck portion, K designates the side wall of the tank in which the roof is used, L designates the bottom of the tank, and X designates the liquid on which the roof floats. The peripheral pontoon A is of annular form, it is provided with aflat bottom N, and it is of stiff construction. The center pontoon is also of stiff construction, but is of circular form. The deck portion B is flexible. The top Wall I of the center pontoon is preferably of substantially cone shape so that water that falls onto same will be discharged onto the deck 3, andthe top wallof the annular pontoon A is preferably inclined downward from its outer edge towards its inner edge, so as to shed water onto the deck portion. Any suitable means can be used to impart rigidity to the two pontoons. In the roof herein shown, the center pontoon is made rigid by means of trusses H arranged on the interior of the same and securely attached to the top and bottom walls*ofsaid pontoom'said'center pontoon having a vertically-disposed peripheral rim J and a bottom M that is flat.

The outer edge of the deck portion B is attached to the inner rim of the peripheral pontoon A in sufficiently close proximity to the bottom of said potoon to cause the underside of said deck portion, at the point where it is joined to said annular pontoon, to be maintained in a wetted condition by the roof supporting liquid, even when the roof is floating normally, with no rain or water load. Usually, the deck portion B will be attached to the annular pontoon A at the level of th supporting liquid X, or at about 1 inch above the surface of said liquid. The inner edge of the deck portion is attached to the extreme lower edge of the rim J of the center pontoon. One or more primary drains l, of any preferred type or kind, are installed in the deck portion B in close proximity to the rim J of the center pontoon, so as to carry off water from the collection trough formed by said rim J and the downwardly pitched deck portion B. A plurality of auxiliary drains or emergency drains 2, of any preferred type or kind, are installed in the deck portion B, preferably in close proximity to the inner rim of the peripheral pontoon A. The roof is erected in side of the tank K, and during the erection operation, the center pontoon and the peripheral pontoon are sustained by supporting structures of such height as to cause the deck portion B and the bottom M of the center pontoon to assume a level or horizontal position when the plates from which said deck portion is formed are joined together and connected to the lower edge of the peripheral rim J of the center pontoon.

As previously stated, my improved construction contemplates the use of trusses for transferring part of the weight of the annular pontoon A to the rim J of the center pontoon, so as to concern trate a heavy load or downward force on said rim, for the purpose of producing a progressively increasing downward slope in the deck portion B as it approaches the peripheral rim of the center pontoon, adjacent to which the primary drain or drains I of the roof are located. In the form of my invention herein illustrated the roof is equipped with a plurality of radial trusses, each of which comprises a vertically-disposed post F projecting upwardly from the center pontoon adjacent the peripheral rim J of same, an inclined rod E extending downwardly and inwardly from the upper end of the post F and attached securely to the center pontoon, an oppositely-inclined rod D extending downwardly and outwardly from the upper end of the post F and attached securely to the inner rim of the annular pontoon A, and a turn buckle G in the rod D.

After the liquid, usually oil, has been pumped into the tank to float the roof, the turn buckles G of the radial trusses D, E, F are tightened to such a degree as to bodily rais the annula pontoon A and transfer a sufiicient portion of the weight of said annular pontoon to the rim J of the center pontoon to submerge the lower edge of said rim and the inner edge of the deck portion that is attached to same, approximately 8 inches deeper than the outer edge of said deck portion which is attached to th annular pontoon A. This concentrated load on the peripheral rim of the center pontoon C deflects the deck portion B below its normal submergence, in a steepening curve, as shown more clearly in Figure 2, whereby said deck portion will be maintained in a position to insure rapid and efiicient drainage. Another desirable feature of such a construction is that any wrinkles that may have existed in the plates of which the deck portion B is constructed, will be removed or pulled out by the downward pull or sag which the rim J of the center pontoon exerts on the inner edge of the deck portion B and by the upward push or pressure which the roof supporting liquid exerts on the underside of the deck portion B, as a result of the downward deflection of the inner edg of said deck portion. Figure 2, which is a diagrammatic view, is intended to illustrate the above described action, and in order to make the principle of operation of the roof clear, I hav made the vertical scale of Figure 2 approximately four times the horizontal scale, and have provided said view with a plurality of vertically-disposed arrows y, of different length, the length of said arrows showing the magnitude of the pressure of the roof supporting liquid on the deck portion B and on the bottom M of the center pontoon as the radius de creases. The down-thrust on the posts F of the radial trusses, plus the above mentioned pressure variation of the roof supporting liquid, causes or produces the progressively increasing downward slope or pitch of the deck portion B towards the rim J of the center pontoon.

Due to the fact that the deck portion is main tained in a steep, downwardly-pitched condition, with its inner edge submerged several inches in the supporting liquid and its outer edge located at or in sufficiently close proximity to the surface of the liquid to be constantly washed or splashed by the liquid, there is little or no liability of the underside of the deck portion of the roof corroding, even when the roof is used on sour or highly corrosive oil.

Having thus described my invention, what I claim as new and desire to secure by Letters Pat cut is:

A floating roof having a stiff outer pontoon, a stiff center pontoon provided with a peripheral rim, a flexible deck portion attached at its outer edge to the outer pontoon adjacent the bottom of said pontoon and attached at its inner edge to the lOWer edge portion of th rim of the center pontoon, and means for causing part of the weight of the outer pontoon to exert a downward force or load on the rim of the center pontoon, said means comprising vertically-disposed posts on the center pontoon located adjacent the rim of the same, and radially-disposed tension members co-acting with said posts and attached at their outer ends to said outer pontoon.

JOHN H. WIGGINS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

